Ion implantation is used in semiconductor manufacturing to create doped layers or to modify a material. Carbon ions are increasingly used for implantation. Implanting carbon ions into a layer of crystallized semiconductor material, such as silicon, can provide a pre-amorphization layer. Carbon ion implantation is also used to provide a barrier, preventing dopant atoms such as boron and phosphorous from out-diffusion.
In conventional approaches to carbon ion implantation, a carbon containing gas such as carbon monoxide (CO) or carbon dioxide (CO2) gas is combined with a carrier gas such as phosphine (PH3). These gases are introduced into an ionization chamber, which is referred to as an arc or plasma chamber. While the gasses are introduced into the chamber, a cathode is heated by a filament and the cathode emits electrons in thermionic emissions. An arc current is applied and arcing occurs between the cathode and the walls of the chamber, ionizing the source gas molecules, creating ions. The ions are drawn out from the ionization chamber through an arc slit or opening using magnetic and electric fields, and are then directed through beam analyzers and focusing elements, and finally are accelerated and impacted onto the target device. As the use of carbon ion implantation increases, problems with oxidation and coating in the ion source head, and failures of the cathode in the ion source head, have been observed.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not drawn to scale.